1. Field of the Invention
The present invention relates to a process for preparing symmetrical dinitrodiphenyl ethers from o- or p-nitrochlorobenzene or o- or p-nitrofluorobenzene.
2. Prior Art
Japanese published patent application No. 56-161354 discloses forming 4,4'-dinitrodiphenyl ether from p-nitrochlorobenzene using a polar organic solvent and a source of nitrite ions and an alkali metal salt of a fatty acid as a base.
The mechanism of the reaction is ##STR1##
The production of 4,4'-dinitrodiphenyl ether via pathway (1) to (2) to (4) has been disclosed in the chemical journal literature since 1975*. Formation of p-dinitrobenzene is the slowest step, and it is an essential intermediate. A variety of bases have been claimed for step (3) Japanese published patent application No. 54-66633 discloses forming 4,4'-dinitrodiphenyl ether from p-nitrochlorobenzene using a polar organic solvent miscible with water, an alkali metal carbonate or acid carbonate, a source of nitrite ions, and water. Reaction (2) is simultaneous with reaction (3) and some sodium nitrite is always consumed. It is both a catalyst and a reagent, and as source of nitrite ion is always specified as an essential ingredient. FNT *Chemistry Letters, pages 1253-1256, published by Chemical Society of Japan (1975).